Many commercially useful microorganisms use glucose as their main carbohydrate source. However, a disadvantage of the use of glucose by microorganisms developed for production of commercially desirable products is the high cost of glucose. The use of fructose and mixed feedstocks containing fructose and other sugars as carbohydrate sources for microbial production systems would be more commercially desirable because these materials are readily available at a lower cost. Desirable commercial feedstocks contain non-glucose breakdown products of starch or a variety of sugars such as fructose, sucrose, and xylose. Low cost feedstock derived from sucrose generally contains fructose and glucose in addition to sucrose.
A production microorganism can function more efficiently when it can utilize any fructose present in a mixed feedstock. Therefore, when a production microorganism does not have the ability to utilize fructose efficiently as a major carbon source, it cannot operate as efficiently. For example, bacterial cells typically show preferential sugar use, with glucose being the most preferred. In artificial media containing mixtures of sugars, glucose is typically metabolized to its entirety ahead of other sugars, including fructose. Thus, when a production microorganism cannot utilize fructose as a carbohydrate source, it is desirable to engineer the microorganism so that it can utilize fructose.
Caimi et al. (U.S. Pat. No. 7,524,660) describe a process for the utilization of fructose by PTS minus microorganisms. The process includes expressing increased fructokinase activity in the microorganisms and optionally, expressing a galactose-proton symporter to increase the fructose transport capacity of the microorganisms. However, there is still a need for further improved fructose utilization in microbial production strains, particularly in the presence of glucose.